Tim
I have a three scaling option Toolbar. Opt #1, Scale-up by 25%, scale down by 80%. Notice the upscale and the downscale are different. As an example, if you scale up an object that is 100 inches long by 25%, your object is now 125 inches long. Now to get back to the exact size, you need to scale down by only 80% of the new size of the model.
However, to scale up by 100% you only need to scale up by 2. And to recover your old size scale down by 50% or .5000
Opt #2 up by 100% down by 50%, to return to the original size.
Opt #3 up by 1.001% down by .999000999. Now, this is exact enough for what I do, however after a while, you will notice the inaccuracies of the up and downscaling.
trans=Geom::Transformation.scaling(center, 1.001)
trans=Geom::Transformation.scaling(center, 0.999000999)
When plugins where much easier to make, I could modify the plugins for my use. However, I can't or won't give out the plugins as they have been modified, and the original are not my creation.
I just wanted to show you that your perception of scaling won't work.
"A simple way around this would be a one-button plug-in that scales the model x1000 and centres it in the viewport. Then, after doing the modelling, clicking the button would scale the model by 0.001 and centre it in the viewport."